A solid polymer-type fuel cell has an ability of generating a high output density and can be operated at low temperature and, therefore, can be reduced in size and weight. Accordingly, the solid polymer-type fuel cell is expected to be put into practical use as, for example, a power source of an automobile, a power source for stationary electric power generation, or a power source for electric power generation of a mobile device.
In a solid polymer-type fuel cell, a pair of electrodes are disposed on both sides of a solid polymer electrolyte membrane having proton conductivity, and electric power is generated by supplying pure hydrogen or reformed hydrogen serving as a fuel gas to one electrode (fuel electrode) and supplying an oxygen gas or air serving as an oxidant to the other electrode (air electrode).
The electrodes of such a fuel cell are constituted of an electrode electrolyte in which a catalyst component is dispersed (hence the electrodes may be called electrode catalyst layers in some cases). The electrode catalyst layer on the fuel electrode side generates protons and electrons from the fuel gas; the electrode catalyst layer on the air electrode side generates water from oxygen, protons, and electrons; and the solid polymer electrolyte membrane ionically conducts protons. Thus, electric power is obtained through the electrode catalyst layers.
Conventionally, in the solid polymer-type fuel cell, a perfluoroalkylsulfonic acid-based polymer represented by Nafion (trademark) has been used as the electrolyte of the electrode catalyst layers. This material is excellent in proton conductivity, but is very expensive. In addition, the material has a large number of fluorine atoms in the molecule thereof and is thereby low in combustibility, which causes a problem to make the recovery and the reuse of expensive noble metal, such as platinum, used in the electrode catalyst very difficult.
On the other hand, various non-perfluoroalkylsulfonic acid-based polymers have been investigated as alternative materials. In aiming to be used at a high temperature condition where the power generation efficiency is high, it has been attempted to use aromatic sulfonic acid-based polymers having high heat resistance as electrolytes.
For example, Japanese Unexamined Patent Application Publication No. 2005-50726 (Patent Document 1) discloses the use of a sulfonated polyarylene polymer as the electrode electrolyte. Furthermore, Japanese Unexamined Patent Application Publication No. 2004-253267 (Patent Document 2) discloses the use of specific sulfonated polyarylene.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2005-50726
[Patent Document 2] Japanese Unexamined Patent Application Publication No. 2004-253267